Ferromagnetic resonance in hydrogenated-dehydrogenated LaNi5, FeTi and Mg2Ni and its relation to magnetic and surface investigations

The intermetallic compounds LaNi5, FeTi and Mg2Ni are Pauli paramagnets and therefore should not show any ferromagnetic resonance (FMR). Nevertheless FMR signals are observed in crushed samples and their intensity increases with the number of hydrogenation-dehydrogenation cycles. The FMR signal shows strong temperature dependence and for the pure Ni compounds it disappears just below the Curie temperature of pure Ni metal. The results are interpreted on the assumption that the FMR originates from superparamagnetic clusters that are formed by precipitating Ni or Fe atoms near the surface. The results are discussed in relation to previous magnetisation and surface measurements. Time-dependent behaviour observed at room temperature supports the superparamagnetic cluster picture, and is used to estimate the distribution of clusters on the surface. An additional narrower line with g = 2.01 +- 0.02 was observed at elevated temperatures and is attributed to magnetic resonance in the paramagnetic state. (author)